1. Technical Field
The present disclosure generally relates to the field of collimation of emitted light as well as transfer of thermal energy. More particularly, the present disclosure is related to a lens support structure and the removal of thermal energy from a compact light-emitting device supported by the lens support structure.
2. Description of the Related Art
High-power direct diode lasers are gaining popularity in applications such as heat treating and cutting in the automobile and material processing industries. To heat or cut a material, the radiance of the diode laser has to be high enough to process the material effectively. Manufacturers of diode lasers have developed single-stack and multi-stack diode lasers with an attached collimating lens to collimate light emitted from the fast-axis of diode lasers. Fast-axis collimation is possible to within a few milli-radians of divergence of the laser beam when a collimating lens is used. A collimating lens is typically a rod lens or high numerical aperture cylindrical lens, and each diode laser typically has a collimating lens attached to the fast-axis, which is placed about a few tens or hundreds of microns in front of a facet of the diode laser.
To maintain a perfectly parallel beam of light, the collimating lens has to be placed within a few tens or hundreds of microns from the diode laser facet, with some variational dependence on the optical working distance of the collimating lens. This requires alignment of the collimating lens with the diode laser. It is not easy to passively align the collimating lens to perfectly collimate the laser beam, and many hours of alignment and special tools are usually required to assemble a diode laser package that includes one or more diode laser and the respective one or more collimating lens. Alternatively, alignment of the collimating lens can be provided via active alignment, in which alignment is provided on a real-time basis. However, active alignment can be particularly difficult for a high-power diode stack due to the large number of closely packaged diode lasers.
In the case of a multi-stack diode laser, each individual diode laser has to be collimated and the respective collimating lens is attached to the diode laser package structure. In aligning each collimating lens, the diode laser is running at the operating current and the collimating lens is aligned with a tooling setup that allows for movement of the collimating lens in a four- or five-axis controlled mechanical stage. After the alignment, the collimating lens is attached to the frame of the diode laser by, for example, UV-curing epoxy or a soldering process. However, failure of diode laser alignment is not uncommon. Typically, alignment of the diode laser fails due to weak bonding of the epoxy or degradation of the epoxy joint caused by thermal cycles of the diode laser.
There is, therefore, a need for a novel mechanical structure to align the collimating lens to provide optimal collimation and to hold the collimating lens in place to withstand many thermal cycles of the diode laser.
Furthermore, compact light-emitting devices, such as light-emitting diodes (LEDs), laser diodes, vertical cavity surface-emitting lasers (VCSELs) and the like, generate thermal energy, or heat, when in operation and hence are heat-generating devices themselves (hereinafter referred to as “compact heat-generating devices” and “heat-generating devices”). Regardless of which type of heat-generating device the case may be, heat generated by a compact heat-generating device must be removed or dissipated from the compact heat-generating device in order to achieve optimum performance of the compact heat-generating device and keep its temperature within a safe operating range. With the form factor of compact heat-generating devices and the applications they are implemented in becoming ever smaller, resulting in high heat density, it is imperative to effectively dissipate the high-density heat generated in an area of small footprint to ensure safe and optimum operation of compact heat-generating devices operating under such conditions.
Many metal-based water-cooled and air-cooled cooling packages have been developed for use in compact packages to dissipate heat generated by the various types of compact heat-generating devices mentioned above. For instance, heat exchangers and heat pipes made of a metallic material with high thermal conductivity, such as copper, silver, aluminum or iron, are commercially available. However, most metal-based heat exchangers and heat pipes experience issues of oxidation, corrosion and/or crystallization after long periods of operation. Such fouling factors significantly reduce the heat transfer efficiency of metal-based heat exchangers and heat pipes. Other problems associated with the use of metal-based cooling packages include, for example, issues with overall compactness of the package, corrosion of the metallic material in water-cooled applications, difficulty in manufacturing, and so on. With increasing demand for high power density in small form factor, there is a need for a compact cooling package for compact heat-generating devices with fewer or none of the aforementioned issues.